This invention relates to a prestroke control device for fuel injection pumps, and more particularly to a device of this kind which controls the prestroke of the plunger by means of a control sleeve sliding on the plunger.
A prestroke control device for fuel injection pumps for use in diesel engines has been proposed, e.g. by Japanese Provisional Utility Model Publication (Kokai) No. 61-118936, which varies the prestroke of the plunger (the stroke from a lift-starting position of the plunger to an injection-starting position thereof), in order to control the fuel injection timing and the fuel injection rate.
The proposed prestroke control device comprises a control rod engaging a control sleeve slidably fitted on a plunger, the control rod being rotatable about its own axis for varying the axial position of the control sleeve relative to the plunger, an engaging member provided at one end of the control rod, and a prestroke actuator engaging the engaging member for rotatively driving via the engaging member the control rod about its own axis.
More specifically, as shown in FIG. 1, the plunger 2 has a fuel passage 5 formed therein, and an inclined groove 6 formed in an outer peripheral surface thereof. The control sleeve 3 is slidably fitted on the plunger 2, which has a spill port 7 formed therein for communication with the inclined groove 6 of the plunger 2. The spill port 7 opens into a fuel chamber 9 defined within a plunger barrel 8 in which the plunger 2 is slidably received.
The control sleeve 3 has a circumferentially extending notched groove 10 formed in an outer peripheral surface thereof, in which is engaged a spherical end 12 of a lever 11 radially outwardly extending from the control rod 4. As the control rod 4 is rotated about its own axis, the lever 11 is pivotally moved in a direction indicated by the arrow B in FIG. 1 to displace the control sleeve 3 in a direction indicated by the arrow A, whereby the prestroke of the plunger 1 varies.
As shown in FIG. 2, the prestroke actuator 14 is coupled to a U-shaped member (engaging member) 19 secured to an end of the control rod 4 to rotatively drive the control rod 4 about its own axis via the member 19. The actuator 14 is controlled by means of a controller, not shown, in response to the rotational speed of an engine associated with the fuel injection pump and the load on the engine.
In the illustrated example, the actuator 14 is essentially comprised of a rotor 16 which is electromagnetically actuated to rotate against the force of a return spring 15 by a required amount. The rotor 16 has an output shaft 17 carrying at its tip an eccentric engaging ball 18 engaged in a U-shaped groove in the U-shaped member 19, whereby the control rod 4 is rotated about its own axis by the actuator 14 when the latter is energized.
In the conventional prestroke control device constructed as above, the control sleeve 3 can be dislocated from its controlled position due to vibrations transmitted from the engine or vibrations generated by the pump per se. The dislocation of the control sleeve 3 is attributable to the fact that the center of gravity of the control sleeve as a moving part is distant from the axis of rotation of the control rod 4 so that when a force (vibrating force) caused by the above-mentioned vibrations acts upon the control sleeve 3, the resulting rotating force is applied to the control rod 4 to cause same to rotate. The dislocation of the control sleeve 3 thus results in a change in the prestroke of the plunger, adversely affecting the injection timing, the injection rate and even the injection quantity, and hence torque fluctuations and degraded exhaust emission characteristics of the engine.